Automatic telephone system



Aug 26, 924; 1,505,963

c. E. LOMAX AUTOMATI C TELEPHONE SYSTEM Filed Sept. 13 1920 2Sheets-Sheet l Jamil [51 Flare E E.LEIIHEX Aug. 26, 1924 1,505,963

C. E. LOMAX AUTOMATIC TELEPHONE SYSTEM Filed Sept. 13 1920 2Sheets-SheeQ 2 \KN mmmmmmmmm @w mnmnmnmnm mnmnmnm SQ wk a W W QNQK NRJim Patented Aug. 26, 1924.

UNITED STATES PATENT. OFFICE.

CLARENCE E. LOMAX, O1 CHICAGO, ILLINOIS, ASSIGNOB TO AUTOMATIC ELECTRICCOMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed September 13, 1920. Serial No. 409,932.

To all whom it may concern:

Be it known that I, CLARENCE E. LOMAX, a citizen of the United States ofAmerica, and a resident of Chicago, Cook County,

5' and State of Illinois, have invented certain new and usefulImprovements in Automatic Telephone Systems, of which the following is aspecification.

- My invention relates in general to automatic telephone .systems, butmore especiallyto automatic systems of relatively small size intendedfor use in factories, department stores, mercantile establishments, andthe like, and commonly known as private automatic exchanges.

The principal object of the invention is to provide in a system of theabove character a new and improved means for restricting the servicewhereby the subscribers are divided 0 into three classes in accordancewith the different kinds of service which they are to be given. Otherobjects relate to the provision of novel trunk circuits for givingspecial service between a private automatic exchange of the abovecharacter and the different ofiices in a multi-oflice manual telephonesystem, and to the provision of various other circuit improvements, allof which will be explained hereinafter, with reference to theaccompanying drawings.

Referring to the drawings, comprising Figs. 1 and 2, I have showntherein by means of the usual circuit'diagrams the essential features ofa private automatic exchange em- 5 bodying the principles of myinvention.

In order to facilitate the explanation it will be assumed that theprivate automatic exchange illustrated is used to give telephone serviceto the oflicials and employees in the 0 various departments of anoperating telephone company. That is, the system is used solely forlocal calls within the companys establishment, and is not in any'senseof the word a public exchange. It will be assumed 5 furthermore, thatthe telephone company in question is operating a large public exchangeof the manual multi-oflice type.

With this understanding the apparatus shown in the drawings may bebriefly del) scribed as follows:

The substation A, Fig. 1, is an automatic substation of the usual typehaving the usual talking instrumentalities and a calling device S forcontrolling the central oflice 5 switches At the private branch exchangeswitchboard the hne conductors 11 and 12 terminate in the individual,line or trunk selecting switch O. The line switch C is a rotary lineswitch of the usual type,whose wipers have no normal position and movein a forward direction only, and is operable responsive to the removalof the receiver at the substation A to extend the associated line intoconnection with a trunk line extending to an idle first selector switch.

One of the trunk lines which is accessible to the line switch C andother similar line swltches is shown in the drawing as extending to thefirst selector D. The selector D is of the well known Strowger verticaland rotary type and when taken for use is adapted to respond to thefirst digit in the called number to select a desired one of the severalmain groups into which the exchange is divided. For this purpose thebank contacts of the selector are arranged in a plurality of levels inthe well known manner and each level may correspond to a differentgroup, It will be assumed herein that the local lines in the privateautomatic exchange under discussion are divided into two groups. Thefirst and second levels of the-selector D and associated selectors arereserved for these two groups of local lines, and trunk lines extendfrom the contact sets in the twolevels to two groups of connectorswitches in the customary manner. There are also trunk lines extendingto the nearest manual ofiice which are used for outgoing calls from theprivate branch exchange to the public exchange and the third and fourthselector levels are reserved for these trunk lines. By a specialarrangement which will be described the trunk lines in the above levelsare combined into one group. One of the outgoing trunk lines comprlsesconductors 105-107, inclusive, which extend from a contact set in thethird level to the repeater 'E, whence the trunk conductors 150 and 151continue to the manual exchange where they terminate in jack J.

One of the local trunk lines, comprising conductors 1014.04, inclusive,is shown in the drawing as extending from the first level of theselector 1) to the connector F, Fig. 2. The connector F is also aStrowger vertical and rotary switch of well known mechanicalconstruction and has a capacity of 100 lines. In view of the fact thatit is desired to use certain contact sets in the connector banlzs forgroups of special trunk lines which Wlll be described shortly, theconnector F 1s provided with means for giving rotary service if desired.Any two 01' more consecutive sets of bank contacts may be combined intoone group in the well known manner and the first idle contact set insuch group may be reached by calling the number assigned-to the firstcontact set in the group. The manner in which the groups are formed willbe explained fully hereinafter. The special trunk lines referred to areprovided princi pally for theuse of'certain clerks in the commercialdepartment of the telephone com pany who have occasion to call the chiefoperators and other employees in the manual ofiices. These trunk linesalso take care of certain trafiic requirements as will be explainedhereinafter. Assuming that there are four manual oflices there may be agroup of five trunks extending to each ofiice. As shown herein thesecond level of the group of connectors which includes the connector Fis reserved for the trunk lines-extending to two of the offices and acertain level in the other group of connectors is used for the trunklines extending to the other two. One of the trunk lines accessible tothe connector F comprises conductors 272274, inclusive, and extends tothe repeater H, whence conductors 275 and 276 extend to one of themanual ofiices and there terminatein the jack J.

. Having described the general layout of-the system, the restrictedservice arrangements therein and the reasons therefor may now be brieflyexplained. As before stated, the subscribers are divided into threeclasses. The subscribers in the first class, comprising a majority ofall those who have telephones, are given local service only. That is,their calls are restricted entirely to the private automatic exchange.The subscribers in the second class can establish local connections andalso have access to the outgoing trunk lines extending to the manualpublic exchange, but are. denied access to the special trunk lines whichextend to the several difierent OfllCQS. The second class willordinarily comprise the difierent department heads and other employeeswhose importance in the company is sufiicient to entitle them 'tooutgoing service. The subscrib'ersin the third class have norestrictions in their service whatever, and can establish allconnections previously re.- ferred to as well as connections to thespecial trunks extending to' the several manual oflices. The third classof subscribers includes the higher oflicialsof the company and also agroup of employees in the commercial department who have occasion to usethe special trunks in transacting routine business with the manualoflices. The above one of which conductors is the conductor 32.

When used in connection with the restricted service system thisconductor is commonly referred to as a discriminating trunk. The classof service given any subscriber is determined by the manner in which theextra wiper of his individual line switch is connected. Three bus-barsare provided at the line switchboard which may be numbered 1, 2, and 3,as shown in the drawing. Bus-bar N o. 1 is permanently connected toground, bus-bar N o. 3 is connected to ground through a resistance ofabout 500 ohms, while bus-bar No. 2 has no ground connections at all.The extra wipers of the several line switches'are connected to thesethree bus-bars in accordance with the class of service to be given tothe respective subscribers. For example, the extra wiper of line switchC is connected to bus-bar No. 3, from which it may be inferred that thesubscriber at substation A belongs to the third class and is givenunrestricted service, as will presently be explained in detail.

The operation of the circuits will now be explained more in detail andforthis purpose the process of setting up a few typical connections willbe described. It will first be assumed that a local connection is to beestablished between substationA as the calling station, and substation Aas the called station.

When the. receiver is removed at substation A a circuit isoompleted'overthe lineconductors 11 and 12 for the line relay 15.

Upon energizing, relay 15 closes at its arma wiper 24 to the abovecircuit at a point midway bet-ween the said relay and magnet. Theoperation now depends upon whether the trunk line with which the lineswitch wipers are associated is busy or is not busy. If this trunk lineis busy there willbe a ground potential upon test contact 28 and therotary magnet 16, being suppliedwith direct ground via the test wiper24', will operate in the manner of a buzzer -to advance the switch.wipers step by step in s'earchof an idle trunk line. It may be assumed,however, that when the call is initiated the trunk line shown in thedrawing is idle. Under these circumstances when the line relay isenergized no trunk selecting movement will take place, the switchingrelay 14 will energize immediately and the stepping magnet will remaininoperative due to the high resistance of the said switching relay. Uponenergizing, the switching relay 14 disconnects the line conductors 11and 12 forming the windings of the line relay 1.5 and from ground,respectively, and extends them by way of armatures 17 and 19, wipers 22and 25, bank contacts 26 and 29, and armatures and 64and their restingcontacts to the windings of the double wound line relay 51 of theselector D.

\Vhen the calling line is extended to the selector D in the manner abovedescribed the line relay 51 is energized over theline circuit and closesa circuit for the slow acting release relay 52. Upon energizing, relay52 prepares a circuit for the vertical magnet 56 at armature 68 and atarmature 66 connects ground to the release trunk conductor 31 therebycompleting a holding circuit for the line switch C which extends byway-of the said conductor, test-contact 28, test wiper 24, armature 18and-its working contact, winding-of the switching relay 14, and thewinding of the stepping magnet 16 to battery. The above circuit isestablished before the slow acting line relay 15 has had time to fallback and serves to maintain the switching rela 14 energized throughoutthe connection. round potential is also extended by Way of the privatenormal conductor 13 to multiple test contacts in the banks of theconnector switches which have access to the line of substation A wherebythe said line is made busy.

The calling subscriber may now operate his calling device in accordancewith the first digit in the desired number which in the present case isthe digit 1. When the calling device is operated the line circuit isinterrupted once momentarily and in response thereto the line relay 51is momentarily deenergized. As a result an impulse of current istransmitted through the slow acting series relay 53 and the verticalmagnet 56 in series, whereby the vertical magnet 56 is operated to raisethe wipers 9093, inclusive, until [they stand opposite the first level.The slow acting relay 53 is energized in series with the vertical magnet56 and at the first upward movement of the shaft closes a circuit forthe stepping relay 54 as follows: ground at G normally closed.- contactsprings controlled by armature 69, working contact of armature 70 andthe said armature interrupter contact 73 of the rotary magnet 57,resting contact of armature 81 and the said armature. ofl' normalsprings 82 and 83, and the winding of relay 54 to battery. Uponenergizing, relay 54 establishes a locking circuit for itself at itsarmature 74, and at its armature prepares a circuit for the rotarymagnet57. At the end of the vertical movement of the switch the slowacting relay 53 is deenergized and since relay 54 remains locked up acircuit for the rotary magnet 57 is completed in an obvious manner. Therotary magnet is therefore energized to advance the switch wipers 93,inclusive, into engagement with the first set of bank contacts in thelevel opposite which they have been brought to rest. At the same timethe rotary magnet opens its interruptervcontaczt 73, thereby breakingthe locking circuit of the stepping relay 54 which accordinglydeenergizes and.

breaks the circuit of the rotary magnet, which then deenergizes also andagain closes its interrupter contact. The operation now depends uponwhether the first trunk line in the first level is busy or is not busy.If this trunk line is busy the test contact engaged by the test wiper 92will have a ground potential upon it and a circuit will be establishedfor energizing relay 54 again. the

said circuit being traceable from the grounded test contact, by Way oftest wiper, 92, armature 62 and its resting contact, interrupter contact73 of the rotary magnet, resting contact of armature 81 and the saidarmature, off normal springs 82 and 83, and theaginding of the steppingrelay 54 to ba tery. ay '54 is accordingly again ener gized and theoperations just described are repeated. Assuming that the trunk lineshown in the drawing and comprising conductors 101-104, inclusive, isthe first idle trunk line, when the wipers of the switch arrive at backcontacts 9598, inclusive, the test wiper 92 will find no ground on testcontact 97 and the stepping relay 54 will not again be energized. Therotation of the switch will therefore cease, and the switching relay 50,which has heretofore remained short circuited, will energize over acircuit which extends from the grounded release trunk conductor 31 byway of the winding of the said switching relay, interrupter contact 73,of the rotary magnet, resting contact of armature 81 and the saidarmature, ofi' normal sp-rings'82 and 83, and the winding of thestepping relay 54 to battery. Due to the high resistance of relay 50,relay 54 is not operated at this time. Upon energizing. relay 50disconnects ground from the line relay armature 65 in an obvious manner,connects the release trunk conductor 31 to the test wiper 92 at armature62, connects the discriminating trunk conductor 32 to wiper 91 atarmature 61, and by means of arm-aitures 60 and 64 disconnects the twoconductors of the incoming line from the windings of the line relay 51and extendsthem by way of wipers 217 and its working contact, ofinormalsprings 213 and 214, armature 229 and its' 90 and 93, ba-nk contacts 95and 98,'conductors 101 and 104, and normally closed contact springs ofthe back bridge relay 200 to the double wound line relay 201 of the connector F, Fig. 2. I

The calling line having been extended to the connector F, line relay 201is energized over the line circuit in the usual manner and completes acircuit for the slow acting release relay 202. Upon energizing, thelatter relay prepares a circuit for the vertical magnet 210 at armature217 and at arma ture 218 connects ground to the release trunk conductor103. By the latter operation a holding circuit is completed extendingback to the selector D by way of the said conductor 103, test contact97, test wiper'92, and armature 62 and its working contact to therelease trunk conductor 31 where it joins the previously describedholding circuit extending back to the line switch C. The circuit overconductor 103 serves to maintain switches C and D in operated positionthroughout the connection.

The subscriber at substation A may now call the second digit in thedesired number which is also the digit 1. By the resulting interruptionin the line circuit the line relay 201 is deenergized momentarily andtransmits an impulse of current tothe vertical magnet 210 over thefollowing path: ground at G, armature 216 and its resting contact,armature 217, and its working contact, ofi normal springs 213 and 215,winding of the vertical magnet 210, and the winding of the slow actingrelay 205 to battery. By the operation of the vertical magnet 210 thewipers 260-263, inclusive, are raised one step until they stand oppositethe first level. The slow acting relay 205 is energized in series withthe vertical magnet and by means of the armature 229 maintains thecircuit thereof intact notwithstanding the fact that the circuit isaltered by the shifting of the off norv mal springs at the first upwardmovement of the switch shaft. At the end of the vertical movement relay205 de'energizes and transfers the operating circuit to the rotarymagnet 211.

The calling subscriber ma now operate his calling device in accor ancewith the third and final digit in thecalled number which we will assumeto be the digit 5'. -'Five interruptions are accordingly produced in the.line circuit to which the line relay 201 responds as before andtransmits a series of five impulses'to the rotary magnet 211 over thefollowing circuit: ground at G, armature 216 and its resting contact,armature resting contact, resting contact of armature of armature 24 4and the said armature, and

the winding of the rotary magnet 211 to battery By the operation of therotary magnet 211 the switch wipers 260-263 are rotated step by step andare finally brought to rest in engagement with the contact setassociated with the line of substation A, this contact set being the setshown. in the drawing and comprising bank contacts 264-267, inclusive.The slow acting series relay 208 is energized in series with the rotarymagnet and during the rotation of the switch connects the test wiper 261with the test relay 207 at its armature 237. At the same time relay 208places'a shunt around the break contact at armature 234 of the testrelay by means of its armature 238 in order to guard against thepossibility of the said test relay being energized during the rotationto break the circuit of the rotary magnet.

It will be assumed first that the line of substation A is busy whenconnected with as above described. Under. these circumstances the test,contact 265 will have a ground potential upon it and when the testwiper 261 engages this test contact, the test relay 207 will beenergized. The rotation of the switch having ceased, the slow actingrelay 208 will now fall back and a locking circuit is closed for thetest relay 207 which includes its armature 233 and normally closedcontacts controlled by armature; 237 of relay 208. The test relay 207also breaks the rotary magnet circuit at its armature 234, and at itsarmature 235 connects a lead from the busy signalling machine to .the

lower heavy line conductor fthereby transmitting an audible busy signalto the calling subscriber. Being'thus advised that the desired line isfor the time being inaccessible, the calling subscriber will hang up hisreceiver. Having explained the operations whic take place when thecalled line is busy, it will now be assumed that the line is idle whencalled. Under these circumstances, when connection to the line iscompleted the test wiper 261 will find. no ground potential upon thetest contact 265 and the test relay 207 will not be energized. Then,when the slow acting relay 208 falls back an instant later, a circuit iscompleted for the switching relay 209 as follows: From the' groundedreleasetrunk conductor 103, by way of normally closed contact springscontrolled by armature 228,;armature 233 and itsresting contact, lowerwinding of relay 209, resting contact of armature 237, wiper 26-1,test'contact 265, conductor 13', winding of switching relay 14', and thewinding of the stepping magnet 16 to battery. Upon the closure of theabove circuit relays 209 and 14 are energized in series and the latterrelay operates to clear the line of substation A of its normal batteryand ground connections in the line switch C. It is noted that dueto amechanical interlocking device controlled by relay which has not beenenergized, thev switching relay 14 is operated only about half way andthe wipersofthe line switch C are 'not connected.

In the connector F, when the switchlng relay 209 is energized'it closesa locking circuit for itself at its armature 241, grounds the test wiper261 at its armature 240, opens the circuit of the test relay 207 atarmature 242, breaks the circuit of the stepping relay 203 (to bedescribed later) at its armature 243, breaks the rotary magnet circuitat its armature 244, and at armatures 239 and 245 connects up the upperand lower line wipers 260 and 263. The connection having been completedringing current from the generator (Jen. is projected intermittently outover the line conductors 311 and 312 to the called substation A in orderto operate the bridged ringer thereat to si al the called subscriber. Itwill be observed that the return path for the ringing current includesthe upper winding of the ring out 01f relay 206, and when'the calledsubscriber responds by removing his receiver the said ring cut off relaywill be operated in the usual manner. Upon energizing, relay 206 looksitself at its armature 231, and at its armatures 230 and 232 0pens theringing circuit and finally completes the talking circuit.

The calling and called subscribers are now connected and may converse asdesired. Talking battery is supplied to the transmitter at substation Athrough the windings of the line relay 201, while talking battery issupplied to the transmitter at substation A through the windings of thedouble wound back bridge relay 200. The latter relay is energized aslong as the receiver remains oil the hook at the called station and inaccordance with the usual practice reverses the direction of currentflow in the calling line. Althou h this reversal of current performs nouse ul purpose in the present disclosure it is a standard arrangementused frequently in the control of measured service apparatus andsupervisory equipment and on that ground has been included.

When the conversation is finished both subscribers will replace theirreceivers. When the receiveris replaced at substation A the line andrelease relays 201 and 202 of the connector F are deenergized and acircuit is thereby closed for release magnet 212 which operates torestore the connector F to normal position in the usual manner. Relay202 also disconnects ground from the release trunk conductor 103 andthereby breaks the holding circuit extending back the same time theswitching relay 14 in the I line switch C is deenergized and the. saidline switch is thus restored to normal also.

Having described the general operation of the switches in the process ofsetting up a local connection I will now describe certain otherconnections, the next to be considered being an outgoing call from theprivate automatic exchange to the public exchange. As hereinbeforestated, the trunk lines extending to the public exchange. which are tobe used for ordinary outgoin service are accessible from the third andourth levels of the selector switches, and these trunk lines are all inone group. The digit to be called therefore in order to obtain anoutgoing connection to the public exchange is the digit 3. Assuming thatthe calling subscriber is the subscriber at substation A, as in theprevious case, when the receiver is removed the line switch 0 isoperated as before to extend the calling line to an idle trunk line.Assuming that the trunk line extending to the selector D is taken forstepping relay 54 is locked up by the operation of'the slow acting relay53 when the,

vertical movement starts, and at the end of the vertical operation thelatter relay falls back to start the automatic trunk selecting movementin order to locate an idle trunk linein the third level. Assuming thatthe trunk line shown in the drawing and comprising conductors 105, 106,and 107, is the first idle trunk line, when the switch wipers arrive atthe bank contacts 110113, inclusive, the rotation of the switch willstop and the switching relay 50 is energized to extend the conductors ofthe calling line by way of wipers 90 and 93, bank contacts 110 and 113,and conductors and 107 to the windings of the double wound line relay121 of the repeater E. I

When the calling line is extended as above explained the line relay 121is energized over the line circuit and closes a circuit for the slowacting release relay 122. Upon energizing, the latter relay closes aholding circuit atits armature 126 which extends by way of conductor106, test contact 112, test wiper 92, and armature 62 and its workingcontact to conductor 31 where the circuit joins the holding circuitextwo sides of the trunk line in series.

tending back to the line switch G. This holding circuit is of coursesimilar to the one established when connection was extended to theconnector F as previously described. Returning to the repeater E, whenthe release relay 122 is energized it closes a chain contact at itsarmature 127 (the purpose of the chain contacts will be 'de' scribedshortly), and completes the connection through to the. trunk conductors150 and 151 by means of its armatures 125 and 128. As soon as the latterconnection is completed the double wound relay 123 will be bridgedacross the trunk line on the outgoing side of the repeater and a circuitis thereby closed for the line relay 152 at the manual oflice. The lineuipment at the manual office consists of t e usual answering jack andlamp with the associated line and cut off relays. The line rela however,should be of high resistance, pre erably about 12,000 ohms, in order toprevent the relay 123 from being operated. Relay 123 is normall groundedat its middle point and it f0 lows that the line relay 152 will beenergized to light the answering lamp L to advise the operator that acall has been received. When the operator answers, the cut off relay 153is energized, the line relay 152 is disconnected and the lamp L isextinguished in the usual manner. Relay 123 is.now energized by currentfrom the cord circuit battery over the lower trunk conductor 151 anddisconnects relay 124 at armature 129. Ground is also disconnected fromthe middle point of relay 123 by the operation of armature 130, and therelay remains held up over It he e operator will now complete theconnection to the desired subscriber in the public manual exchange inany suitable manner. Since these operations are old and well understoodno further explanation thereof need be ven.

When the conversation is ended and the subscribers hang up theirreceivers the connection is released automatically so far as theapparatus in the private automatic exchange is concerned the same as wasdescribed in the case of a local connection.'

In view of certain operations which take place at the repeater E,however, it may be well to explain this a little. When the receiver isreplaced at substation A the line and release relays 121 and,122 aredeenergized and the latter breaks the holdin circuit extending back tothe selector in order to restore the said selector and the line switch Cto normal. At-the same time relay 122 disconnects the double wound relay123 from in bridge of the trunk conductors 150 and 151. By thisoperation the operator at'themanual oflice is given a disconnect signalin the usual manner and relay 124 is connected to the upper trunkconductor 150. Relay 124 is now energized by ground from the cordcircuit and will remain energized as long as the plug remains in, thejack. At its armature 131 relay 124 again grounds the release trunkconduct-or 106' in order to make the trunk line busy. When the operatorpulls down .the connection in response to the disconnect signal groundis disconnected from the upper trunk conductor 150, relay 124 isdeenergized and the trunk is cleared and made accessible to other calls.

' As stated hereinbefore, both the third and fourth levels are used fortrunk lines to the public exchange and it will now be explained owaccess is had to the trunks in the fourth level in caseall the trunklines in the third level are busy. Although not mentioned before it willbe understood that in order to accomplish this the selector D isprovided with a vertical test wiper which is indicated in the drawing bythe reference character 94 .and which is adapted to test over a strip ofvertical test contacts during the vertical operation of the switch. Inthe present disclosure, however, only one of these test contacts, whichis the third level test contact 114, is inguse. When all the trunk linesin the third level are busy conductor 116 is grounded by way of chaincontacts in the repeaters as will be readily seen. The contact atarmature 127 in the repeater E is one of these chain contacts and thecontacts at armat-ures 117, 118, etc., are similar contacts in the otherrepeaters of the group. Although not shown herein, each of the otherrepeaters has a contact similar to 132 which is adapted to shunt itscontact such as 117. Thus,

when all of the trunk lines in the third level are busy chain contactsin all the repeaters will be closed, conductor 116 will be grounded andrelay 115 will be energized to connect ground to the Vertical testcontact 114. With this explanation the operation of the switch inraising its wipers to the fourth level may be briefly explained.Assuming the same conditions as in the previous case, in which thewipers of the switch were raised to thethird level by calling the digit3, the stepping relay 54 having been energized at the start of thevertical movement, when the slow acting relay 53 falls back at the endof the vertical movement this relay ordinarily closes a circuit for therotary magnet 57 bythe retraction of its upper armature 70. 'In thepresent case, however,

ing of relay 55 to battery. Upon energiz-.

in'g, relay..55 connects the release trunk conture grounded after relay,53 has again energized, closes a locking circuit for itself at itsarmature 80, disconnects a shunt from around the vertical magnetinterrupter contact 76 by means of its armature 81, and at itsarmature'79 transfers the operating circuit from the rotary magnet 57 tothe vertical magnet 56. Thevertical magnet is accordingly energized overthe following cir-. cuit: from the grounded release trunkcon-v ductor31, by way of the working contact of armature 78 and the said armature,armature 75 and its working contact, armature 79 and its workingcontact, winding of the slow' acting relay 53, and the winding of thevertical magnet 56 to battery. By the operation of the vertical magnetthe switch wipers are raised one step until they stand opposite thefourth level. In operating, the vertical magnet opens its interruptercontact 76 and thereby breaks the locking circuit of the stepping relay54 which accordingly deenergizes and at its armature 75 breaks thecircuit of the vertical magnet which thereupon deenergizes also andagain closes its interrupter contact. The switch is thus adapted forfurther vertical operation in case there is one or more levels in thegroup in addition to the third and fourth. In the present case, however,since the fourth level is the last levelin the group the vertical test'contact associated therewith will not be grounded and relay 55 willdeenergize as soon as the vertical test wiper leaves the test contact114. The slow acting relay 53 is energized in series with the verticalmagnet 56 and as soon as either the vertical magnet deenergizes to closeits interrupter contact or relay 55 falls back to close its contact atarmature 81, it is immaterial which occurs first, the said relay 53again closes an energizing circuit for the stepping relay 54 whichaccordingly pulls up and locks itself as usual. An instant later theslow acting relay 53 is deenergized and as a result the usual circuitfor the rotary magnet 57 ,is completed in order to initiate the trunkhunting movement on the fourth level. From now on the operations are thesame as have already been described. It will be understood of coursethat as many levels as desired may be combined into one group. Whenoperated in accordance with the digit corresponding to the first levelof the group the selector D will automatically hunt Vertically until itfinds an idle level after which the switch will rotate automatically inthe usual manner to select an idle trunk in the selected idle level.

Considering now the restricted service feature, it has been explainedbefore that the subscribers in class 1 are denied access to the outgoingtrunks to the public exchange. In order to accomplish this result theselector D to the third or fourth level.

is provided with a pair of shaft controlled springs 85 and 86 which areadapted to be closed by the shaft when the same is raised way ofoperating these springs is to mount will be actuated by the circular cupspring casing which is attached to the top of the shaft. Assuming nowthat a call is made to the public exchange, when the wipers of theselector D are raised to the third level the shaft springs 85 and 86will be closed. Then, when the slow acting relay 53 falls back at theend of the verticalmovement a circuit will be completed through therelease magnet 58 as follows: from .conductor 33, in the line switch 0,by way of the extra wiper 23, bank contact 27, discriminating trunkconductor 32, shaft springs 85 and 86, armature 67 and its workingcontact, armature 72 and its resting contact, the lower pair of offnormal springs, and the winding of the'release magnet 58 to battery. Ifthe calling subscriber is the subscriber at substation A or anysubscriber'in the third class the conductor 33, or correspondingconductor, will be connected to the bus-bar No. 3 and ground will besupplied to the discriminating trunk conductor 32 through a 500 ohmresistance. Due to the fact that this resistance is included in thecircuit the release magnet 58 will not energize and the call will gothrough as described. The same is true if the calling subscriber is asubscriber in the second class, for in such case no ground at all willbe connected to the discriminating trunk conduc-.

tor 32. If the calling subscriber is a subscriber in the first class,however, the conductor corresponding to conductor 33 will be connectedto direct ground at bus-bar No. 1, and since direct ground is thussupplied to the discriminating trunk conductor 32 the release magnet 58will be energized when the slow acting relay 53 falls back at the end ofthe vertical movement of the switch and the switch will be restored tonormal position. Thus it will be seen that subscribers in the firstclass cannot make outgoing calls to the public exchange. I

The process of establishing connections over the special trunk lines tothe several manual oflices will now be considered. As before stated,there are two groups of these trunk lines which terminate in the secondlevel of the group of connectors which includes the connector F, Fig. 2.In order to permit of the selection of idle trunk lines the connector Fis adapted to operate as a rotary connector and to this end it isprovided with an extra test wiper 262 and associated bank of testcontacts. The wiring of the test contacts which is required in order totake care of the groupingof the trunks is A convenient the second levelis shown. The upper row of contacts are the ten regular test contacts ofthe level, the next lower row of contacts are the ten special testcontacts provided to take care of the rotar feature, whilethe two bottomrows are t e line contacts. In order to combine a plurality of contactsets into one group, all that is necessary is to connect the two testcontacts of each contact set except the last, as is shown clearly in thedrawing.

We will assume now that some subscriber in the third class wishes adirect connection with one of the oflices in the public exchange withouthaving to go through one of the regular outgoing trunks. The callingsubscriber may be an employee of the commercial department or otheremployee who wishes to call either the chief operator or the wire chiefat the distant manual office, or he may be an official of the compan whowishes a direct connection with a new to obtaining quicker service thanwould be possible if the call were trunked through in the ordinarymanner. At any rate, and regardless of who the calling party is, we mayassume that the call is coming from the substation A, which is a class 3telephone. Access to one of the connectors, the connector F, forexample, is obtained in the usual manner by raising the receiver andthen calling the digit 1. Since the required group of trunk linesterminates in the second level the next digit to be called is the digit2. In response to the calling of this digit the vertical magnet 210 isoperated under control of the line relay 201 to raise the wipe-rs260-263, inclusive, to the second level. Assuming now that the requiredoflice is the ofiice wrved by the first group of trunk lines in thesecond level the next digit to be called will be the digit 1, or thedigit corresponding to the first contact set in the group. When thecalling device is operated for the final digit 1 then, the rotary magnet211 is energized once and the wipers are advanced into connection withbank contacts 26827 1, inclusive. The slow acting relay 208 is energizedin series with the rotary magnet 211 and connects the test wiper 261 tothe test relay 207. Assuming that the first trunk line is busy, testcontact 269 will have a ground otential upon it and the test relay 207will be energized, establishing a locking circuit for itself at itsarmature 233, and opening the rotary magnet circuit at its armature 234.Since the trunk line now connected with is the first trunk line in thegroup the extra test contact 270 will be connected to test contact 269as shown, and when the slow acting relay 208 deenergizes a circuit forthe stepping relay 203 is completed as follows: from the grounded testcontact 27 0, by way of test wiper 262, armature 236 and its restingcontact, armature 243 and its resting contact, interrupter contact ofthe rotary magnet 211, winding of the stepping relay 203, and thewinding of the slow acting relay 205 to battery. As a result of theclosure of the above circuit relays 203 and 205 are ener ized, thelatter-relay being effective to shift the locking circuit of the testrelay 207 from the release trunk conductor 103 to the test wiper 261, bymeans of its armature 228. Relay- 203, upon energizing, establishes alocking circuit for itself at its armature 220 and .at its armature 221closes a circuit for the rotary magnet 211 in an obvious manner. Therotary magnet 211 is accordingly energized and rotates the switch wipersinto engagement with the next set ofbank contacts. In operating, therotary magnet 211 opens its interrupter contact and thereby breaks thelocking circuit of the stepping rela 203, which accordinglyfallsback'and brea s the rotary magnet circuit, whereupon the rotarymagnet deenergizes and again closes its interrupter contact. If the nexttrunk line is busy the test wiper 262 will still engage a grounded testcontact and the stepping relay sis 203 will again be energized and theoperation 1 above described will be repeated, the rotation being thuscontinued until the switch wipers arrive at an idle trunk line. lVhenthis occurs the rotation will cease due to the failure of rela 203 toagain pull up, the test relay 207 wi l deenergize, and the switchingrelay- 209 will be operated.

The foregoing describes the operation when the trunk selecting movementis required. For convenience it will be assumed that when the call ismade the first trunk line in the group, or the one shown in the drawing,is idle. stances, when the wipers of the switch come into engagementwith the bank contacts Under these circum- 268-271, inclusive, the testwiper 261 will wiper 261, test contact 269, conductor 273,

resistance 281, and the upper winding of relay 278 to battery. Upon theclosure of the above circuit the switching relay 209 of connector F isenergized with the usual results, but relay 27 8 1n the repeater H,being marginally adjusted, is not energized due to the inclusion ofresistance 281 in the circuit. The line wipers 260 and 263 having beenconnected up by the energization of the switching relay 209,. a circuitis completed for the ring out ofl relay 206 of the connector F asfollows: ground at G, normally I closed contacts controlled by armature282 ofrelay 279, lower winding of relay 278, conductor 272, bank contact268, line wiper 260, armature 239 and its working contact,

armature 230 and its resting contact, and

the upper'winding of relay 206 to battery.

By the closure of the above circuit the cut oil relay 206 is energizedto disconnect the ringing circuit and complete the talking con nectionin the usual manner. Relay 27 8 is also energized now, since its twowindings assist each other and by means of its armatures 285 and 287extends the trunk conductors 272 and 274 by way of the condensers to theoutgoing trunk conductors 276 and 275, respectively. By this operationthe upper winding of relay 279 is bridged across the trunk conductors inorder to operate the line relay 295 at the A board in the distant manualofiice. Relay 279 is energized in series with the line relay 295, but ismade somewhat slow to pull up by means of its short circuited lowerwinding in order to provide plenty of time for the operation of the ringcut relay 206 in the connector, and in order to permit relay 278 tobecome fully operated before the circuit through its lower winding isbroken. After relay 279 is operated relay 278 is held up by means of itsupper winding. Relay 279 also disconnects the ring down relay 280 fromacross the line. When the A operator perceives the lighted lamp L shewill answer the call by plugging into the jack J and will then completethe connection to the desired party in the well known manner.

When the connection in the private automatic exchange is released relay278 will fall back and open the trunk circuit at its armatures 285 and287. This operation disconnects relay 279 "from in bridge of the trunkconductors 275 and 276 and thus gives the operator a disconnect signalin response to which she will pull down the connection. The trunk lineis then ready for use in another call. V

The special trunks such as the one shown herein are also intended foruse in handling special traflic calls from the manual exchange to theoffices of the telephone company. This may be explained as follows:

There are always a certain number of sub-- scribers whose service hasbeen temporarily discontinued because of their failure to pay theirtelephone bills or for other proper reasons and the answering jacks ofsuch subscribers are properly marked in order to indicate to the Aoperators that the associated subscribers are to be denied service. Whena call is received from a subscriber of this class the A operator is notpermitted to talk to him herself but is required to connect thesubscriber with the proper clerk in the commercial department who isable to look up the records and explain to the subscriber why he is notpermitted to make a call. The special trunks are used to take care ofthe 'trafiic to the commercial department under the circumstancesdescribed above and for this purpose the answering jacks associated withsuch trunks at the A board are mul tipled throughout the board. Inaddition each trunk line has a lamp signal, lamp L in the case of thetrunk line shown. in the drawing, and all these lamps are located at aconspicuous place in the commercial department where they. may readilybe seen by all the record clerks. The lamps assoclated with each groupof trunk lines are of a distinctive color and all the lamps are wired toa pilot relay which is arranged so as to sound an alarm whenever anylamp comes in. Suppose now that one of the A operators in the manualoffice to which the trunk line shown in the drawing extends, receives acall from a subscriber who is denied service. The operator answers thecall by connecting the subscriber with the trunk line shown, through themedium of jack J or a multiple thereof, and then rings on the trunk. Bythis operation the ring down relay 280 in the repeater H is energizedand establishes a locking circuit for itself at its lower armature. Atthe same time the lamp L is lighted and the pilot relay 288 actuates thealarm. The record clerks, of whom there may be one for each of themanual oifices, on hearing the alarm will all glance up at the bank oflamps to see from which otfice the call is coming; the clerk who has therecords of that office will then answer the call by calling the numberof the trunk, the connection being completed through the medium of theconnector F or a similar connector in the manner described previously.lVhen the connection is completed the circuit of relay 280 is broken atarmature 286 of relay 278 and relay 280 is deenergized to put out thelamp L It would seem at first glance that some confusion would resultdue to the fact that the connector F is a rotary connector and the trunkline shown is only one of a group of five similar trunk lines any one ofwhich might be used. Such is not the case, however, except under unusualcircumstances. Considering any particular group vof trunks, the severaltrunk lines of the group are connected to the jacks at the A board ininverse order and the last trunk therefore is always used for aconnection of this kind. The commercial clerk who answers the call willnot call the number of the trunk group, but on the contrary will callthe number of the last trunk in the group. For example, suppose that acall is received on the trunk whose number is 125, this being the lasttrunk in the first group in the second level of the group of connectorswhich includes the connector F. The clerk will answer the call bycalling the number 125, and if another call is receivedbefore the clerkhas disconnected; it will come in on trunk 124. After hanging up thereceiver and disconnecting from trun number 125. the clerk may nowcallthe number 124 in orderto answer the'second call.

7 In view of the fact that connections of the class described arehandled by skilled em- 10 ees of the telephone company there is tt 0chance of any trouble or'confusion.

- The restricted service arrangement at the connector switch may now beexplained. As

,explained hereinbefore there s .only one class of subscribers who haveaccess to the special trunks. These are the subscribers in class No. 3,and the subscribers in classes 1 and 2 are denied access to such trunks.In

' calling party is at substation A and such being the-case the line maybe extended by way of the line switch C and the first selec tor D to theconnector Fin the manner previously explained. When connection isextended to the connector F the discriminating trunk connector 32 isextended thereto also by means of armature 61 ofrelay 50, wiper 91, bankcontact 96 and discriminatlng trunk conductor 102, and the winding ofthe discriminating relay 204 to battery. Since the calling subscriber isa subscriber in class 3 a 500 ohm ground will be placed on thediscriminating trunk conductor and relay 204 will be energized. By theoperation of relay 204 conductor 102 is connected to shaft springs 225and ground is disconnected therefrom. The connector F may now beoperated in the'usual manner to raise its wipersto the second level.When this occurs the shaft springs 225 and 226 are closed. At

* the end of the vertical movement of the switch the slow acting relay205, which was energized in series with the vertical magnet, isdeenergized and a circuit is comp eted -which extends from thediscriminating trunk conductor 102 by way of armature 223 and itsworking contact, shaft springs 225 and 226, armature 227 and its restingcontact, and the winding of the release magnet 212 to battery. Theclosure of the above circuit is without effect, however, because of thefact that the discriminating trunk conductor 102 is connected to groundthrough a resistance of 500 ohms. The release magnet 212 is thereforenot energized and the call is permitted to go through as described inthe foregoing paragraphs. Supposenow that the calling subscriber is asubscriber in class 1. The operations which take place when the call isattempted will be precisely as described in the preceed- 'ing caseexcept that direct ground will be placed on the discriminating trunkconductor 102, and when the slow acting relay 205 deenergizes therelease magnet 212 Wlll be operated to release the connector. It will beevident then that a subscriber in class 1 cannot obtain access to thespecial trunks.

If the calling subscriber is a subscriber in the second class, when theconnection is attempted no ground at all will be applied to thediscriminating trunk conductor. In this case relay 204 wi 1 not beenergized and the shaft spring 225 will remain connected to ground atarmature 224 of the said relay 204. In this case when the slow actingrelay 205 falls back at the end of the vertical movement of the switch acircuit will be completed for the release magnet as in the previouscase, except that the circuit is grounded locally within the connectorF, and the release magnet will be operated to restore the connector F tonormal. Thus subscribers in the second class are also prevented flrom;connecting with the special trunk lines. I

There is one other feature which may be described, when it is believedthat the explanation will have been completed. This feature has to dowith the use of one of the special trunk circuits as a watchmans servicetrunk. When used in this manner the trunk is reached from a set of bankcontacts in one of the local levels and except for this the circuit maybe precisely as shown in the drawing. The relay which corresponds to theilot rela 288, however, will, in this case, he indivi ual to the trunkand may be arranged so that when operated it will serve to close analarm circuit includa number of gongs or other signals lomg cated atsuitable points on the premises. If the watchman desires to make anoutgoing call at any time during the night he may do so from'anytelephone within reach regardless of whether such phone is arranged foroutgoing service or not. At the manual ofiice the trunk is not onlyequipped with the usual answerin jack and lamp but it has the usualmultlple at the B board like an ordinary subscribers line, and the number assigned to this trunk is the number" used for calling the companysremises after business hours. Y

When a cal is Toceived the various gongs'or signals are operated in a'manner which will be readily understood and the watchman, no matterwhere he happens to be,-is notified thatsomebody is calling him. He willthen answer the call by calling the number assigned to the trunk fromthe nearest phone in the branch exchange, and since the trunk istermlnated in one of the local levels'he can do this from any telephone.This is a great convenience as otherwise the watchman would have to goarranged for outgoing service and a telephone of this kind might not beas accessible as the more numerous telephones which are arranged forlocal service only,

Having described my invention, what I consider to be new and desire tohave protected by Letters Patent will be pointed out in the appendedclaims.

What l claim as my invention is: i

l. in a telephone system, selector andconnector switches for connectingcalling and called lines, service restricting means for each line,service restricting means in the selectors, and service restrictingmeans in the donnectors, the said means cooperating to divide thesubscribers into three classes in accordance with the kinds of servicethey are entitled to.

2. In a telephone system, subscribers lines divided into three classesaccording to the kinds of service they are entitled to, serially d llrelated selector and connector switches for establishing localconnections, a. group of trunk lines accessible to said selectors,another group of trunk lines accessible to said connectors, servicerestricting means individual to each line, service restricting means inthe selectors cooperating with said individual means for preventing thesubscribers in one class from connecting with the first group of trunklines, and service restricting means in the connectors cooperating withsaid individual means for preventing the subscribers in another classfrom connecting Wlblll the second group oi trunk 3. In a telephonesystem, a central exchange comprising serially related selector andconnector switches for connecting calling and called lines, a group oftrunk lines accessible to said selectors, another group of trunk linesaccessible to said connectors, and service restricting means in theexchange dividing the subscribers into three classes, the subscribers ofone class being denied access to the first group of trunk lines and thesubscribers of two classes being denied access to the second group oftrunk lines,

4t. In a telephone system, a private automatic exchange, a publicmulti-ofiice exchange, two groups of t lines extending from the privateautomatic exchange to two different ofiices of the public exchange,respectively, two serially related groups of automatic switches fromwhich said two groups of trunk lines are accessible, respectively, andservice restricting means including mechanism in the switches in each ofsaid groups dividing the subscribers of said private automatic exchangeinto three classes,the subscribers of one class being reto a telephonewhich was 5. in a telephone system, a private auto matic exchange, apublic multi-ofiice exchange, outgoing trunk lines extending from theprivate exchange to the nearest office in the public exchange, selectorswitches a to which said trunks are accessible, a group of special trunklines extending from the private exchange to each ofiice in the publicexchange, connector switches to which said special tpunks areaccessible, local lines accessible to said connectors but not to saidselectors, and service restricting means including mechanism in saidswitches dividing the subscribers of said private exchange into threeclasses, the subscribers of one class being restricted to local callsonly, the subscribers of another class being restricted to local callsand regular outgoing calls, while the subscribers of the third class areunrestricted and can establish local calls, regular outgoing calls, andcalls over said special trunk lines,

6. In a telephone system comprising a plurality of manual oifices, aprivate auto.- matic exchange, a group of special three digit trunklines from the privateexchange to each manual otfice for giving directservice between the private exchange and the manual ofices, anothergroup of one digit trunk lines between the private exchange and thenearest manual oflice for handling ordinary outgoing calls from theprivate exchange, selectors for handling calls to said one digit trunklines, connectors cooperating with said selectors for handling calls tosaid three digit trunk lines, service restricting means, and releasemechanism in each of said switches automatically responsive to releasesaid switches, when they are operated in an attempt to obtainconnections to which the calling subscribers are not entitled 'Z. in atelephone system, a private exchange including automatic switches, incoming trunk lines accessible to each of said switches, distinctivesignals associated with said ilfllilk lines and operable when calls arereceived thereover, and ing any received calls by directively operatingone of said switches to connect with the trunk line associated with thesignal which is operated, said means including an automatic telephone,and automatic progressively movable switching mechanism. for connectingsaid telephone to the first idle one of said switches.

8. in a telephone system, a manualexchange, and an automatic exchange, atwoway trunk line connecting said exchanges means for answer andaccessible to automatic switches in the automatic exchange, means forcalling the automatic exchange over said trunk line from the manualexchange including means for operating a signal associated with the saidtrunk without making the trunk line busy, means for answering the callby directively operating one of-said switches to connect with said trunkline, and means for operating the same or another one of said switchesto extend a connection to the manual exchange over said trunk line afterthe first connection is released.

9. In a telephone system comprising a plurality of manual oflices, aprivate automatic exchange, special trunk lines connecting said exchangewith each of said oflices, automatic switches having access to saidtrunk lines in the said exchange, distinctive signals associated withsaid trunks at the sald exchange, the said signals being oper-, ablewhen calls are received and being located so as to be perceived by aplurality of individuals, and means whereby when any call is receivedthe individual whose duty it is to answer the call may do so bydirectively operating the first idleone of said switches to connect withthe trunk line associated with the signal displayed.

10. In a te ephone system, a plurality of lines, a distinctive signalassociated with each line, said signals being responsive to incomingcalls, an automatic progressively movable switch in which all of saidlines are terminated, a plurality of similar switches, a calling devicefor operating one of said switches in accordance with the number of anyline to answer a call received thereover, and an automatic huntingswitch for connecting said calling device with the first idle one ofsaid switches.

11. In a telephone system, a plurality of lines, a distinctive signalassociated with each line, means for operating the associated signalwhen a call is received over any line, an answering telephone common toall of said lines and normally disconnected, an

automatic progressively movable "switch having access to all of saidlines, and a callmg device associated with said telephone for generatingseries of'impulses for operating said switch to connect the said--te1e'- phone with any line to answer a call there'- over when theassociated signal is displayed.

12. In a telephone system, a plurality of lines, an automatic switchhaving access to said lines, means for operating said switch to connectwith any line'to extend an outgoing call thereover or to connect withany line to answer an incomin signals at opposite ends of each 0 saidlines responsive to incoming and outgoing calls, respectively, and meansin said switch for actuating the outgoing call signals or disabling theincoming call signas, depending upon whether the switch is, in use foroutgoing or incoming calls. 4

13. In a telephone system, a two-way.

trunk line having a terminal at one end with by means of manualoperators equipment to answer incoming calls from the automaticexchange, a terminal for said trunk in the automatic exchange, and anautomatic progressively movable switch for connecting with said lastmentioned terminal to answer calls incoming from the manual exchange.

.Signed byme at Chicago, Cook county,

Illinois, this 8th day of September, 1920,

CLARENCE E. LOMAX.

call,

